Method of monitoring and controlling the oxygen blowing process



H. KRAINER ET AL 3,372,023

March 5, 1968 METHOD OF MONITORING AND CONTROLLING THE OXYGEN BLOWING PROCESS Filed May 18, 1965 United States Patent C METHOD or MONITdRI1 IG AND CONTROLLING THE OXYGEN BLOWING rnocnss Helmut Krainer and Jurgen Maatsch, Essen, Germany,

assignors to Beteiligungs und Patentverw'altungsgesell- The present invention relates to a method of monitoring and automatically controlling the reactions occurring in the oxygen blowing process between the metal bath, the slag and the gas phase.

In the oxygen blowing processes for the production of steel, depending upon the composition of the pig iron, the latter is refined in about to minutes with approximately 45 to 65 m. NTP oxygen per each ton of pig iron, whereby one part of the oxygen may also be added in the form of ores. Depending upon the composition of the pig iron, besides the carbon, other undesirable accompanying elements, such as silicon, phosphorus, sulphur, etc. must be removed during the refining process. Essentially, these substances are in the slag in the form of oxide compounds. For this purpose, the formation of a slag of suitable composition is required.

Since the oxygen blowing processes take place at a relatively high speed, the ingredients remaining in the finished steel, particularly phosphorus and sulphur, depend not only upon the thermodynamic equilibria, but particularly upon the reaction speed, which, in turn, is dependent upon the mass-transport-processes. During processing of, for example, pig iron having a high phosphorus content, the formation of a suitable slag must be reached at an early stage. The mass exchange at the interface between the metal bath and the slag can be enhanced by a stirring effect of the carbon oxide rising from the metal bath, as well as by the additional mechanical agitation by means of the oxygen jet.

The slag formation and the stirring action are dependent, on the one hand, upon the manner, in which the blown-in oxygen enters into a chemical and mechanical reciprocal action with the metal bath and the slag, and, on the other hand, upon the fact whether the oxygen reacts directly or by way of the slag with the metal bath, and also, how the oxygen is distributed in the metal bath onto the individual components, such as carbon, silicon, phosphorus, iron, etc.

Apart from the chemical composition and the temperature of the metal bath, as well as the chemical composition and amount of the slag, the metal bath is essentially affected by the characteristics of the oxygen blowing jet, in the area of impingement, such as the momentum of the stream and the stream density.

A characterizing measure for the slag formation and the reactions between the slag and the metal bath is the distribution of the oxygen blown onto the metal bath upon the reactions with the carbon of the metal bath,

and upon the other reactions, which lead essentially to a binding of the oxygen with the slag, if one disregards the reactions over the gas phase, for example, the desulphurizing reaction.

A characteristic for the distribution of the oxygen blown onto the metal bath, with respect to the various reactions, is the ratio of the oxygen amount bound in the carbon of the metal bath per time unit, denoted dO /dt, i.e. the

3,372,623 Patented Mar. 5, 1968 speed of oxidation of the carbon, to the amount of oxygen blown in per time unit, dO /dL, i.e. the oxygen flow rate, O =dO /dt:O /dt:d0 /dO If this characteristic becomes unity, this means that the entire blown oxygen reacts with the carbon of the metal bath; if is smaller than unity, this means that only part of the blown oxygen reacts with the carbon in the metal bath, while the remainder passes into the slag; if, finally 0,, is larger than unity, then the total blown oxygen, as well as additional oxygen from the slag reacts with the carbon of the metal bath, which additional oxygen has been added earlier, for example, in the form of oxide compounds and/or in the form of ores. If the characteristic 0 is known at any time during the course of reaction, it can be used for monitoring and automatically controlling the oxygen blowing process.

It is, therefore, one object of the present invention to provide a method of monitoring and controlling automatically the reactions taking place in the oxygen blowing process between the metal bath, the slag and the gas phase, wherein by means of various values, continually measured and fed into an electronic or other computer, and relating to the oxygen flow rate, the waste gas stream, as well as to the chemical composition of the waste gases with respect to carbon monoxide, carbon dioxide, oxygen and hydrogen, a characteristic 0 for the distribution of oxygen for the reactions occuring in the reaction vessel is calculated according to about the following equation:

1 V O, [0.766-CO+1.266(CO +O In the equation for the characteristic 0,, dO /dt means the amount of oxygen blown onto the metal bath per time unit, namely the pressurized oxygen jet stream, V represents the flow rate of dry waste gases converted to standard conditions, e.g. 0 C. and one atmosphere, and C0, CO 0 and H the volumetric percentage values of carbon monoxide, carbon dioxide, oxygen and hydrogen, respectively, contained in the dry exhaust gases within the gas exhaust system of the reaction vessel. The hydrogen content has to be considered only, if substantial amounts are formed owing to a reaction of carbon monoxide with water vapor in the gas exhaust system at a point located upstream of the taking of a gas sample.

The oxygen distribution can be altered during the blowing process within a wide range and can be adjusted to a value favorable for the metallurgical course of the process by changing the distance between the blowing nozzle and the metal bath surface and/ or the pressurized oxygen jet stream, which both affect the momentum and the stream density of the pressurized oxygen jet within the region of impinging.

Another control can further be obtained by feeding additives to the bath.

For the control of the process, a desired value is fed to set value transmitter for the characteristic of the oxygen distribution 0 and with the aid of this desired value for the characteristic of the oxygen distribution 0,, the pressurized oxygen jet stream and/or the distance between the blowing nozzle and the metal bath surface, and/ or also the feeding of additives, are controlled during the course of the process.

Preferably, the desired value for the oxygen distribution characteristic 0 set either manually or by feeding a function, variable according to the duration of the oxygen blow, into an electronic computer or like means.

In addition to the characteristic of the oxygen distribution 0 other measured values can also furnish information on the prevailing metallurgical conditions of the metal bath and of the slag in the reaction vessel. It is, therefore, advantageous to correct the aforementioned function variable with the oxygen blowing time for the desired value of the characteristic of the oxygen distribution O by further measured values, for example, the temperature of the metal bath, the intensities of certain frequencies of the converter noise, the conductivity between the oxygen blowing lance, suspended in an electrically insulated manner, and the metal bath, the speed of the carbon removal, and amount of the carbon removed from the metal bath, respectively.

Since the characteristic of the oxygen distribution is obtained with a certain indication delay, depending overwhelmingly upon the speed of the applied gas-analysis process, it is furthermore advantageous to control step by step the pressurized oxygen jet stream, the distance between the jet nozzle and the metal-bath surface, as well as the addition of additive substances, and furthermore, to stop intermittently after each control step, depending upon the delay of the indication.

With these and other objects in view, which will become apparent in the following detailed description, the present invention will be clearly understood in connection with the accompanying drawing, wherein the sole figure is a schematic, preferred practical embodiment designed for performing the method according to the present invention.

Referring now to the drawing, a converter 3 contains a metal-slag bath 4 and is provided with conventional inlet and outlet openings. An oxygen blowing lance 1 projecting into the converter 3 in conventional manner feeds the presurized oxygen indicated by the arrow 2 onto the metal-slag 4, and reacts there substantially with the metalloids contained in the pig iron, as carbon, phosphorus, silicon, etc. The converter waste gases created during the reaction of the oxygen with the carbon, which waste gases are indicated by the arrows 5, are caught in a gas receiving hood 6 and are fed through cooled conduits 7, for instance into a waste heat boiler 8. In further gas cooling devices 9 and in a dust remover 10 the gases are cooled and cleaned. The cooled and cleaned waste gases are fed off by means of a blower 11. The oxygen blowing lance 1 is equipped with a device 12 for lifting and lowering, and an indicating device 13 indicating the lance position. A feeding device 14 serves for the feeding of additives into the converter.

The oxygen characteristic 0 is defined by the ratio between the amount of oxygen dO /dt reacting with the carbon of the metal bath per time unit, i.e. the speed of oxidation of the carbon, and the amount of oxygen blown onto the metal bath per time unit,dO /dt, namely the oxygen flow rate The determination of the oxygen flow rate takes place in a pressurized oxygen feeding conduit 16, connected with the oxygen blowing lance 1 by means of a connecting tube 15 by a presure measurement at the point 17 and a temperature measurement at the point 18 and a differential pressure measurement at the point 19. The determined measured values are electrically transmitted to one electronic computer 21, as indicated by the arrows 20.

The computation of the oxidation speed of the carbon is carried out according to the equation dO /dt=K- V(co+c02) Wm Z red) wherein K is a constant, V denotes the volume of the dry exhaust-gas stream calculated and converted to normal conditions (0 C. and 1 atm.); CO and CO are volumetric percentage values of carbon monoxide and carbon dioxide, respectively, in the dry exhaust gas; co and CO red are, in turn, volumetric percentage values of carbon monoxide and carbon dioxide of the exhaust gas when in the converter 3 before the feeding of air at the point 26.

The determination of the volume of the dry exhaust gas stream V takes place in the gas conduits 7 with the aid of a pressure measuring point 22 disposed beyond the dust separator 10, a temperature measuring point 23 and a difierential pressure measuring point 24. The values of the volume of the waste gas stream obtained by these measurements are transmitted electrically to the electronic computer 21, as indicated by the arrows 25.

The waste gas analysis required for the calculation of the oxidation speed of the carbon of the metal bath in the converter 3, without the subsequent entrainment of air through the opening 26 between the gas catching hood 6 and the converter 3, takes place by the taking of gas samples from the gas conduit 7 prior to reaching the waste-heat boiler 8 by a sampling tube 27, since the taking of gas samples at or from the converter 3 would necessitate relatively complicated equipment.

After the dust cleaning and drying of the gas samples, their analysis for carbon monoxide, carbon dioxide, oxygen and hydrogen takes place in the analysis devices 28, wherefrom the determined values are likewise electrically transmitted with a delay of about 10 seconds to the electronic computer 21, as indicated by the arrows 29.

In dust-removing processes, where the combustion of the residual carbon monoxide in the exhaust gases is considerably suppressed before dust removal, the CO content assumes occasionally high values, while the 0 content, originating from the entrained air at 26, will become very low, that is, moves toward zero.

In contradistinction, in processes operating with complete combustion of the carbon monoxide contained in the exhaust gases and with excess of air in the exhaust gas stream, the CO content becomes very low that is, moves toward zero, while the 0 content becomes greater than zero. Consequently, the oxygen content present in the exhaust gases owing to the entrainment of additional air in the exhaust gas has to be taken into account and relied upon for correcting the CO and CO values gained from the analyses.

Since after the ignition of the pressurized oxygen stream in the converter 3 no more free oxygen is available in the converter aside of the oxygen blowing stream and furthermore generally the penetration depth of the air entering the converter 3 through an opening 26 does not sufiice to react in any appreciable degree with the metal-slag bath 4, a consideration of such reactions can be omitted in the calculation of the oxidation speed of the carbon. Furthermore, the impurities of the pressurized oxygen stream can be neglected, since they are generally low.

Jointly with the values for carbon monoxide, carbon dioxide, oxygen and hydrogen from the analyzing devices 28 and a nitrogen content determined as a residue in accordance with the equation and the oxygen originating from the ambient air according to the equation which has subsequently reacted with carbon monoxide to form carbon dioxide; and also considering a reaction between water vapor and carbon monoxide in the exhaust gas system, the corrected analysis values are obtained, as indicated in the equations CO+2O (air, CO +H Simultaneously with these two equations for co and CO red as well as with the equation for the speed of oxidation of the carbon, one obtains and thence o o 766-CO-i-1 266( +02 100 dO /dt 2 By integration of the value the amount of oxygen 0 discharged in the exhaust gases, together with the carbon, in the time period t to t can be calculated.

All measuring values fed into the electronic computer 21, as well as the intermediate and end values calculated therefrom, such as the pressurized oxygen stream, the amount and the composition of the waste gases, etc. are indicated and recorded, respectively on indicating and recording devices 30 continuously.

For the control of the process, a desired value for the characteristic of the oxygen distribution 0 during the blowing of oxygen is fed into the set point transmitter 31 either manually or by way of an empirically obtained function depending upon the oxygen blowing time, as indicated by the arrow 32.

As additional correction values for the desired input, measuring values 33 are fed into the transmitter 31, which measuring values render information regarding the prevailing metallurgical state of the metal-slag bath 4 within the converted 3, such as, for example, the temperature of the metal bath, the intensity of particular frequencies of the converter noise, the conductivity between the oxygen blowing lance 1, suspended in an electrically insulated manner, and the metal bath, the speed of the carbon removal and the carbon amount burnt in the metal bath, respectively.

The pressurized oxygen stream is controlled by an oxygen valve 34 acted upon by a controller 35; the position of the oxygen blowing lance 1 with its lifting and lowering device 12 is controlled by the way of a controller 36, and the feeding of additives by means of the feeding device 14 is controlled by means of a controller 37. In all three control cases, upper and lower limiting values are preset, as indicated by additional arrows 38.

Because the characteristic for the oxygen-distribution is indicated with a certain delay, e.g., of sec., it is favorable to raise and to lower, respectively, stepwise the oXygen blowing lace 1 and/or to increase and to throttle the oxygen supply stepwise, respectively. The same expedient is applied when feeding additives thereto. After each control step, the control function ceases for a short time period, for example, 20 seconds, whereby the length of this time period is a function of the indication delay.

While we have disclosed one embodiment of the present invention, it is to be understood that this embodiment is given by example only and not in a limiting sense, the scope of the present invention being determined by the objects and the claims.

We claim:

1. A method of monitoring and controlling automatically the reactions occurring during the oxygen blowing process between the metal bath, the slag and the gas phase, comprising the steps of measuring continuously the amount of oxygen blown onto the metal bath per time unit and the volume of the waste gas and analyzing said waste gas for C0, CO 0 and H transmitting said measured and composition values for computation and obtaining a value O characteristic for the distribution of oxygen in the occurring reactions according to the equation 0 =m'm O2) O.234H 26.582] andcontrolling the course of the reactions by controlling the O =value, including controlling the amount of oxygen blown onto said metal bath, and the distance of the oxygen nozzle from said metal bath and the feeding of adin per unit of time, V denotes the flow rate of dry waste gases converted to standard conditions, and C0, CO 0 and H denote the volumetric percentage values of carbon monoxide, carbon dioxide, oxygen and hydrogen, respectively, contained in the dry exhaust gases within the gas exhaust system of a reaction vessel.

2. The method, as set forth in claim 1, which includes the step of controlling said O =value in a manner to increase said value in proportion with the increase of the blown oxygen reacting with the carbon in said metal bath.

3. The method, as set forth in claim 1, wherein said step of controlling the cause of the reactions is performed step-by-step.

References Cited UNITED STATES PATENTS BENJAMIN HENKIN, Primary Examiner. 

1. A METHOD OF MONITORING AND CONTROLLING AUTOMATICALLY THE REACTIONS OCCURRING DURING THE OXYGEN BLOWING PROCESS BETWEEN THE METAL BATH, THE SLAG AND THE GAS PHASE, COMPRISING THE STEPS OF MEASURING CONTINUOUSLY THE AMOUNT OF OXYGEN BLOWN ONTO THE METAL BATH PER TIME UNIT AND THE VOLUME OF THE WASTE GAS AND ANALYZING SAID WASTE GAS FOR CO, CO2, O2 AND H2, GRANSMITTING SAID MEASURED AND COMPOSITION VALUES FOR COMPUTATION AND OBTAINING A VALUE OC, CHARACTERISITIC FOR THE DISTRIBUTION OF OXYGEN IN THE OCCURRING REACTIONS ACCORDING TO THE EQUATION OC=1/100 . V/(DOB/DT) . (0.766(CO) + 1.266(CO2 + O2) 0.234(H2) - 26.582) AND CONTROLLING THE COURSE OF THE REACTIONS BY CONTROLLING THE OC=VALUE, INCLUDING CONTROLLING THE AMOUNT OF OXYGEN BLOWN ONTO SAID METAL BATH, AND THE DISTANCE OF THE OXYGEN NOZZLE FROM SAID METAL BATH AND THE FEEDING OF ADDITIVES, RESPECTIVELY, WHEREIN OC DENOTES THE RATIO OF THE OXYGEN AMOUNT BOUND IN THE CARBON OF THE METAL BATH PER UNIT OF TIME TO THE AMOUNT OF OXYGEN BLOWN IN PER UNIT OF TIME, DOB/DT DENOTS THE AMOUNT OF OXYGEN BLOWN IN PER UNIT OF TIME, V DENOTES THE FLOW RATE OF DRY WASTE GASES CONVERTED TO STANDARD CONDITIONS, AND CO, CO2, O2 AND H2 DENOTE THE VOLUMETRIC PERCENTAGE VALUES OF CARBON MONOXIDE, CARBON DIOXIDE, OXYGEN AND HYDROGEN, RESPECTIVELY, CONTAINED IN THE DRY EXHAUST GASES WITHIN THE GAS EXHAUST SYSTEM OF A REACTION VESSEL. 